This invention relates to electromagnetic contactors and to auxiliary switches used therewith. More particularly this invention relates to improved exteriorly mounted auxiliary switches which do not have physical connection to the operating structure of the contactor. Still more particularly this invention relates to top adder and side mounted auxiliary switches of the aforedescribed type which produce logic level electrical output signals.
Electromagnetic contactors are utilized to switch three phase electric power to a load device such as an electric motor or the like. The contactor comprises three pairs of contacts, one for each phase, within a housing. The contactor housing is provided with means for attachment of an additional contact block, usually on the top or front face of the housing. The additional contact block has its own movable contact assembly which is connectable to the movable contact assembly and electromagnet armature of the contactor to operate the additional set of contacts in conjunction with operation of the primary contacts. The sides of the electromagnetic contactor housing have window openings and provisions for mounting auxiliary switch units to the sides of the contactor housing. The auxiliary switch units are customarily mechanically operated units each having a linearly slidable plunger which has operative physical connection with the movable contact assembly and electromagnet armature of the contactor through the respective window opening. Each of the side mounted auxiliary switch units and the top mounted add on contact block have individual contact members, each of which have springs for providing contact pressure in the contact closed positions. Each of these springs introduces a cumulative force which must be overcome by the electromagnet prior to sealing of the armature to the core, thereby requiring that the electromagnet be designed to provide sufficient force for effecting closing of the maximum number of auxiliary contacts. Moreover, the use of mechanically operated contact mechanisms introduces additional friction and component wear to the device as well as affecting contact electrical and mechanical wear and erosion.
In present day intelligent and diagnostic electrical control systems, it is desirable to provide current information to the system controller as to the status of the various control elements, such as an electromagnetic contactor. It is desirable that the system controller know whether the contactor is operated to a closed condition whereby the armature is sealed to the electromagnet core or if the contactor is in the open position wherein the armature is biased away from the electromagnet core. This could be detected with an electromechanical auxiliary switch wherein one set of contacts are closed when the contactor armature is sealed to the core and another set of contacts are closed when the electromagnetic contactor armature is biased away from the core. However, as aforedescribed, the additional spring and frictional forces as well as the component wear of the electromechanical devices are not desirable. Moreover, the controller is commonly microprocessor based such as a personal computer, programmable controller or the like, and the signals to be provided to the microprocessor should preferably be at the logic level magnitude, not readily attainable in electromechanical devices.